Optical communication networks often require monitoring and testing of the various fiber links and/or optical pathways that make up the optical network to ensure the validity, continuity, and status of such fiber links and pathways. For example, optical links require monitoring to detect disconnections, physical breaks, and faults so that corrective action can be taken. It is often the case that service providers must install expensive equipment, such as termination equipment, at a customer's site to monitor its optical network links and fibers. Alternatively, optical network service providers may dispatch a maintenance crew to a customer's location for testing and monitoring purposes, which is both expensive and time-consuming.
U.S. Pat. No. 7,778,554 describes a cost-effective way to monitor optical network links. Generally speaking and referring to FIG. 1 of the '554 patent reproduced here as FIG. 1 (prior art), the technology discussed in the '554 patent involves over-coupling an amplitude modulated signal onto a transmission line 1, such as on a transmission fiber 3, emanating from a first end of the transmission line at a transmitter/receiver device 7. At a second end of the transmission link, the small amplitude modulated portion of the overall signal on the transmission line is then returned to the first end of the transmission line along a receive fiber 5. The second end of the transmission line includes two coupling elements (13,15) that collectively remove the small amplitude modulated signal from the transmit line and then superimpose the amplitude modulated signal on the receive line for return to the transmitter/receiver 7 at the first end of the transmission link. A detector device 11 then compares the small signal to a threshold to determine if the received signal level is too low.
Notably, the solution set out in the '554 patent can only determine if there is an error in the entirety of the path to and from the originating end of the transmission line. Stated differently, because the signal is only monitored for an error at the originating end of the path, the signal must traverse both the transmit and the receive paths and there is not a way to isolated those paths. Hence, there is no mechanism whereby an error can be isolated to the transmit line or the receive line. Moreover, there is no mechanism to determine the signal strength at the receiving end and thus only of the transmit line. It is with these observations in mind, among others, that various aspects of the present disclosure were conceived and developed.